The disclosures about Menwith Hill raise new questions about the extent of British complicity in U.S. drone strikes

THE NARROW ROADS are quiet and winding, surrounded by rolling green fields and few visible signs of life beyond the occasional herd of sheep. But on the horizon, massive white golf ball-like domes protrude from the earth, protected behind a perimeter fence that is topped with piercing razor wire. Here, in the heart of the tranquil English countryside, is the National Security Agency’s largest overseas spying base.

Once known only by the code name Field Station 8613, the secret base — now called Menwith Hill Station — is located about nine miles west of the small town of Harrogate in North Yorkshire. Originally used to monitor Soviet communications through the Cold War, its focus has since dramatically shifted, and today it is a vital part of the NSA’s sprawling global surveillance network.

For years, journalists and researchers have speculated about what really goes on inside Menwith Hill, while human rights groups and some politicians have campaigned for more transparency about its activities. Yet the British government has steadfastly refused to comment, citing a longstanding policy not to discuss matters related to national security.

Now, however, top-secret documents obtained by The Intercept offer an unprecedented glimpse behind Menwith Hill’s razor wire fence. The files reveal for the first time how the NSA has used the British base to aid “a significant number of capture-kill operations” across the Middle East and North Africa, fueled by powerful eavesdropping technology that can harvest data from more than 300 million emails and phone calls a day.